1. Field of the Invention
This invention relates to a fixed-focus imaging lens that forms an optical image of a subject on an imaging device, such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), and to an imaging apparatus, such as a digital still camera, a cellular phone with a camera, an information mobile terminal (PDA: Personal Digital Assistance), a smartphone, a mobile game machine, and a tablet terminal, on which the imaging lens is mounted to perform photography.
2. Description of the Related Art
As personal computers became owned by many families and the like in recent years, digital still cameras, which can input image data of a landscape, a portrait and the like obtained by photography into the personal computers, have rapidly spread. Further, camera modules for inputting images became often mounted on cellular phones, smartphones and tablet terminals. Such equipment having an imaging function uses an imaging device, such as a CCD and a CMOS. As the size of the imaging device became small in recent years, the total size of imaging equipment and the size of an imaging lens to be mounted on the imaging equipment also need to be reduced. Further, since the resolution of the imaging device has become higher at the same time, the imaging lens needs to have high resolution and high performance. For example, the imaging lens needs to have performance corresponding to high resolution of 5 megapixels or higher, and desirably performance corresponding to 8 megapixels or higher.
To satisfy such need, Japanese Unexamined Patent Publication No. 2012-155223 (Patent Document 1) discloses a lens system consisting of seven lenses, which are a relatively large number of lenses, to reduce the total length of the lens system and to increase resolution.